Small beetles are causing big problems in Southern California. Two closely related species, the polyphagous shot hole borer and the Kuroshio shot hole borer (collectively referred to as invasive shot hole borers), have been attacking more than 60 species of trees. These invasive beetles create a series of tunnels, or galleries, where they lay eggs and cultivate a Fusarium fungus to use as a food source. The fungus causes branch dieback, general tree decline, and can result in tree death. The beetles have been found in Los Angeles, Orange, Riverside, San Bernardino, Ventura, Santa Barbara, and San Diego counties.
What should you look for?
- Perfectly round entry holes about the size of the tip of a ballpoint pen
- Wet staining, gumming, white powdery exudate, or frass associated with holes
- Dead or wilting branches on trees
- Author: Ben Faber
Come Learn About Field Identification of Invasive Shot Hole Borers
We're holding two early December trainings on invasive polyphagous and Kuroshio shot hole borer biology, identification, surveillance, and management of infested trees and downed wood. We'll cover these topics in the classroom, then head outside to see infested trees and learn how to identify signs of shot hole borer damage, set up a monitoring program, and sample trees.
$30.00 Registration fee includes lunch, a ISHB Field Guide, and ISHB Demonstration Kit
Continuing Education Units from DPR have been requested, check back for updates.
Speakers include Sabrina Drill, UCCE Natural Resources Advisor; Bea Nobua-Behrmann, UCCE Research Scientist; Kim Corella, Forest Pest Specialist, CalFire; and Paul Rugman-Jones, Research Entomologist, UC Riverside.
Ventura County - Ojai - Dec.6
Meiners Oaks (Ojai) Class & Field Training at Saint Thomas Aquinas Church
Thursday December 6, 2018, 10am – 2:30pm
Los Angeles County - Gardena - Dec. 7th
Gardena Class & Field Training at Gardena Moneta Mason Lodge & Gardena Willows Wetland Preserve
Friday December 7, 2018, 10am – 3:00pm
- Author: Beatriz Nobua Behrmann
[Originally published in the Fall 2018 issue of the Green Bulletin. Modified slightly from original.]
Invasive wood-boring beetles are attacking hundreds of thousands of trees in southern California, including commercial avocados, and trees within urban landscapes and wildland environments.
The invasive shot hole borers (ISHBs) consist of two closely related and morphologically identical species of beetles in the genus Euwallacea: the polyphagous shot hole borer and the Kuroshio shot hole borer. Despite their small size (1.8–2.5 mm) (Figure 1), these beetles are causing big problems in Southern California: they are responsible for the fast decline and death of thousands of urban trees, riparian natural forests, and avocado groves.
The beetles bore into trees, creating a series of small galleries (Figure 2). Inside these galleries, they lay eggs and “farm” a fungus (Fusarium spp.), which is their main food source. The fungus colonizes the trees' vascular systems, blocking transport of water and nutrients. This causes a disease called Fusarium dieback that manifests as branch dieback, general tree decline and, in many cases, tree death (Figure 3).
Both insect species are believed to have been accidentally introduced into California via wood products or shipping materials from southeast Asia. Since ISHBs were first identified in Los Angeles County in 2012, the infestation has spread to 6 other counties: Orange, San Diego, Ventura, Santa Barbara, San Bernardino, and Riverside. Once the beetles arrive at a new location, they colonize susceptible host trees and spread to neighboring areas, infesting more and more trees. Movement of infested firewood and green waste are additional ways the beetles may be transported, allowing them to colonize new areas.
Currently, there are 64 confirmed species of trees in which the beetles can successfully grow their fungus and complete their life cycle. Susceptible trees include many of the species commonly used for landscaping; like sycamores, oaks, cottonwoods, and box elder, among many others. UC Riverside researchers found that ISHBs can successfully colonize trees that were previously considered non-suitable hosts by entering and reproducing in canker-infested branches. Canker is another tree disease caused by fungal or bacterial pathogens that enter the tree through open wounds; it typically causes localized dead areas on the trunks and branches, with sunken, discolored bark and, sometimes, dark lesions.The ISHB beetles can establish their galleries and grow their population in the weakened margin of the canker-infested tissue of some of their hosts. Regular monitoring and removal of canker-infested branches is recommended for these tree species. To find the full list of ISHB reproductive hosts (including the canker-associated hosts) please visit pshb.org.
How do you determine if a tree is infested with ISHB?
Correct identification of the pest is the first step for a successful IPM program. The following are typical symptoms of an ISHB infestation:
- Beetle entry holes: When the beetles excavate their galleries in the trees they make perfectly round small holes, 0.8 mm wide, each roughly the size of the tip of a medium ballpoint pen. (Figure 4)
- Symptoms associated with holes: Entry holes are usually accompanied by one of these symptoms: wet staining, gumming (Figure 5), white powdery exudate (Figure 6), or frass (boring dust). Each species of tree exhibits different symptoms.
- Dieback: Dead or wilting branches can be signs of a severe infestation. If you see dieback on your trees, check for entry holes on the branches or the branch collar.
Best management practices
ISHB-infested trees can quickly become a public safety hazard. Trees with heavily infested branches are especially hazardous, since the combination of tissue decline caused by the fungal pathogen and the mechanical damage from the beetle's galleries weakens the wood, causing limbs to break and fall.
Early detection is the key to controlling this pest. So far, no effective preventative treatments have been reported, so regular monitoring is recommended to ensure infestations are managed early, before they cause dieback or death. Regular monitoring also ensures that trees get treated when they are lightly infested and have the most chances of overcoming the infestation. Researchers continue to study different methods for chemical and biological control of this pest. If you suspect you are dealing with an ISHB infestation, contact your local Agricultural Commissioner's office or IPM Advisor for treatment advice.
Trees that are severely infested (with more than 150 beetle attacks and ISHB-related branch dieback; Figure 7) are not likely to recover from the infestation and will become a constant source of beetles that can disperse and infest neighboring trees. Furthermore, weakened branches on such trees pose hazards to people and property. Therefore, severely infested trees should be removed as soon as possible and their wood properly disposed of. Even after an infested tree is removed, ISHBs can continue to live and reproduce in the stump, so following tree removal with stump grinding is always recommended.
Disposing of infested wood
Borers can survive in cut wood for weeks or even months. It is vital to take care of green waste appropriately in order to avoid spreading this pest to new areas. The most recommended practice is to chip infested wood to a size of 1 inch or smaller; this will kill 95% of the beetles. To ensure the elimination of all beetles and fungal spores within wood, you must solarize infested wood chips with a clear tarp. Other effective disposal methods for infested materials include composting, burning at a biogeneration facility, and use as alternative daily cover within landfills. Untreated chips can be used as mulch, but only in areas that are already heavily infested with ISHB. If chipping is not possible, logs should be kiln dried or solarized under a clear tarp to ensure total beetle elimination. Visit pshb.org for more information on solarization and composting guidelines.
ISHB and its associated fungal diseases can be accidentally spread into new areas by the same people who are trying to manage the problem. Make sure you disinfect your tools after pruning (spraying them with 70% ethanol solution works well), and always cover infested material when moving it to a different location (for instance, for treatment) to avoid spreading the pest./span>
- Author: Ben Faber
This is the most recent activity summary of a group of organizations working on the Invasive Shot Hole Borers and their associated fungal symbionts. This pest/disease complex affects avocado along with a large number of native and landscape plants in California, as well as in other parts of the world (http://ucanr.edu/sites/pshb/; http://ucanr.edu/sites/pshb/files/238251.pdf):
Invasive Shot Hole Borers
Quarterly Situation Report
January through March 2018
Education, outreach, and monitoring activities were robust during the cool damp winter months of 2018. Infestations continued to dominate Orange, San Diego, and Los Angeles counties, with lesser activity in Ventura and Santa Barbara counties. The need for funding of research, education, outreach, and waste management associated with ISHB was brought to the attention of state governance. Preventative efforts to increase awareness of ISHB in unaffected counties continued. Collaborative efforts of numerous agencies, educational institutions, and non-profit groups resulted in the successful efforts listed below.
The two-day Invasive Species Summit was held in the State Capitol for legislators and their staff to learn about environmental pressures and costs created by these species statewide. Three pieces of proposed legislation were written either specific to or with components addressing ISHB. They are: AB 2054 (Gonzlez Fletcher), AB 2166 – California Farm Bill, AB 2470 (Grayson) – Invasive Species Council.
The Statewide SHB Network convened telephonically to discuss ISHB, spread, threat, and help educate those in unaffected counties. An ISHB presentation was given at a statewide horticultural convention in northern California.
The triennial California Native Plant Society Conservation Conference was held near Los Angeles International Airport. ISHB was addressed at a pre-conference invasive species workshop, throughout the conference by tabling and poster session, and during the Invasive Species Session.
UCCE San Diego helmed a two-part GSOB/ISHB-FD webinar, along with other UCCE and CALFIRE collaborators. The first installment streamed in March.
UCCE San Diego began work on an online ISHB survey assessment tool that will be accessible when completed on PSHB.org. This feature will help the public determine if tree symptoms may be due to an ISHB infestation. An added component will allow UCCE to monitor reporting. The decision tree that is part of the assessment takes the reporter to part of the site whereby photos can be submitted if the tool determines a probability of ISHB infestation. This tool will be completed, tested, reviewed, and posted to the website by summer 2018.
San Diego County
- Two ISHB public educational events were presented
- Buy It Where You Burn It campaign distributed literature countywide
- Four ISHB public educational events were presented
- Numerous trap and monitoring sites are established throughout the county primarily in wildlands and parks
- Orange County Waste and Recycling learned 28% of all trees at Prima Deshecha Landfill in San Juan Capistrano are infested with ISHB/FD or Botryospaeria. Most of the vegetation at this site is comprised of native species
- A post-incident GSOB/ISHB reconnaissance was conducted in Weir Canyon, where the Canyon II Fire burned in autumn 2017
- Orange County Parks continued to track tree losses and costs associated with ISHB infestations on its properties. An economic report was publicly released
Los Angeles County
- Three ISHB public educational events were presented
- A funding request was submitted to County governance to continue the ISHB trapping program coordinated by the Resource Conservation District of the Santa Monica Mountains
- The Huntington continued monitoring and green waste processing at the 207-acre facility. An ISHB trapping trial by principal investigator at UC Riverside was initiated that utilizes castor wood as the attractant
- Twenty-six traps are established and monitored in the Santa Clara River watershed extending from the estuary to Piru
- Fifteen traps are established and monitored in the Ventura River watershed. This number is down by two after being lost during the Thomas Fire
- A new infestation was identified in the City of Santa Paula proximal to a known infestation in the Santa Clara River
- One ISHB educational event was presented to Master Gardeners
Santa Barbara County
- Seven traps are being monitored in Montecito and the City of Santa Barbara
- Three traps in Montecito were lost from the January debris flow disaster
- One ISHB educational event was presented to Master Gardeners
San Luis Obispo County
- One ISHB educational event was presented to Master Gardeners
A. Raver. The tiny menace. Landscape Architecture Magazine. March 2018.
Shot Hole Borer galleries, cottonwood
Shot Hole Borer entry point, sycamore. Curtis Ewing, CAL FIRE
- Author: Tunyalee Martin
UC ANR Integrated Pest Management Program
A sugar volcano is one symptom that shows your avocado tree might be infected with Fusarium dieback, a fungi spread by a beetle called the shothole borer. But what you might see if your tree is being attacked by shothole borer, varies among the different kinds of tree hosts. The symptoms—staining, sugary exudate, gumming and beetle frass—are often noticed before the tiny beetles (1.5–2.5 mm) are found.
As its name suggests, these beetles bore into trees. Near or beneath the symptoms, you might notice the beetle's entry and exit holes into the tree. The female tunnels into trees forming galleries, where she lays her eggs. Once grown, the sibling beetles mate with each other so that females leaving the tree to start their own galleries are already pregnant. Males do not fly and stay in the host tree.
Shothole borers have a special structure in their mouth where they carry two or three kinds of their own novel symbiotic fungi. Shothole borers grow these fungi in their tree galleries. It's these fungi that cause Fusarium dieback disease, which interrupts the transportation of water and nutrients in the host tree. Advanced fungal infections will eventually lead to branch dieback.
Early detection of infestations and removal of the infested branches will help reduce beetle numbers and therefore, also reduce the spread of the fungus.
- Chip infested wood onsite to a size of one inch or smaller. If the branch is too large to chip, solarize them under a clear tarp for several months
- Avoid movement of infested firewood and chipping material out of infested area
Avocado is one tree host. Shothole borers successfully lay eggs and grow fungi in many tree hosts, with some of these trees susceptible to the Fusarium dieback disease. For more information about tree host species, where the shothole borer is in California, and what symptoms look like in other tree hosts, visit the UC Riverside Eskalen Lab website.
Californians can help in the fight against invasive species by learning and participating during California Invasive Species Action Week, June 2–10.
During the week, spend your lunch with us learning the latest about invasive tree killing pests, aquatic nasties like quagga mussels and nutria, and how the invasive weed/wildfire cycle is altering our ecosystems! http://ucanr.edu/sites/invasivelunch/
Content in this post taken from the UC IPM Avocado Pest Management Guidelines. Faber BA, Willen CA, Eskalen A, Morse JG, Hanson B, Hoddle MS. Revised continuously. UC IPM Pest Management Guidelines Avocado. UC ANR Publication 3436. Oakland, CA.
And more about Shot Hole Borers